[time-nuts] True Position GPSDP + Rb X72

Bob kb8tq kb8tq at n1k.org
Sun Sep 24 08:30:43 EDT 2017


> On Sep 23, 2017, at 9:39 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> kb8tq at n1k.org said:
>> If the main use is feeding test gear (and not direct synthesis) an Rb may do
>> pretty well. Most instruments assume a dirty reference signal and clean it
>> up internally.  
> What's the bandwidth on the typical cleanup PLL?  How well does that match 
> the noise from a Rb?

It’s like any other PLL with noise involved. You look at the noise of the Rb, the 
noise of the particular cleanup oscillator, and your system requirements. In some
cases that comes out to a few seconds. For Time Nut grade with a really good 
OCXO you are at some pretty long numbers. 

If the Rb starts at 2x10^-11 at 1 second and goes down by square root tau: At
100 seconds you are at 2x10^12. Still not as good as a really good OCXO. At 
10,000 seconds you might get to 2x10^-13 (but probably will not). Your OCXO
likely will climb out of the “parts in 10^-13” range before 10,000 seconds. 

Lots of fun.


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